Aluminum base alloy article



ALUMINUM EASE ALLOY ARTICLE William A. Anderson, Verona, Pa, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application duly 9, 1953 Serial No. 367,094-

7 Claims. (Cl. 148-32) This invention relates to aluminum base alloy articles which have unique softening characteristics in response to annealing.

As is well known, aluminum in common with many other metals becomes harder and stronger at the expense of ductility when it is rolled, pressed, or otherwise deformed within a temperature range that does not permit the formation of new grains. It is also well recognized that the strain created by such deformation can be relieved by heating the worked product to a temperature between 640 and 670 F. Such a thermal treatment is commonly referred to as annealing and the change brought about in the internal structure of the metal is known as recrystallization, i. e., the formation of new crystals from the grain fragments created by the deformation. The occurrence of recrystallization, as recognized by those skilled in the art, is detected by microscopic examination of a properly etched specimen and observing whether new grains or crystals have been formed from the grain fragments. The presence of new grains in substantial numbers may also be detected by the X-ray diffraction method. Further, a marked change in strength and elongation accompanies the formation of new grains. Tensile tests to determine these properties therefore provide a practical and rapid means of learning whether recrystallization has taken place. Although recrystallization of aluminum occurs within the foregoing temperature range it is possible to obtain this result at a lower temperature depending upon the duration of the treatment, the purity of the metal and the extent to which the metal has been deformed or cold worked. The lowest temperature at which a new strain-free grain structure replaces the distorted grain structure of the cold worked metal is known as the recrystallization temperature. Even though the recrystallization temperature of very high purity aluminum may be below 640 F. it has generally been considered impractical, from a manufacturing standpoint, to employ such low temperatures or a range close to them for effecting recrystallization because of the length of time required, the danger of obtaining non-uniform results, and the attendant increase in cost.

As has been mentioned above, the purity of aluminum influences its temperature of recrystallization. For example, metal of a purity of 99.998% has been reported to recrystallize at 212 F. within a period of 6 to 10 minutes following a reduction in thickness of about 91% by cold rolling. The commercial exploitation of such super purity metal is of course limited by its cost and the amount which is available. Hence, even if such high purity metal were otherwise satisfactory, it would not be a competitor of low purity material when large quantities are required. Also, the advantage of a low recrystallization temperature found in high purity metal is lost as the impurity content reaches the level found in metal of ordinary purity.

Although a low recrystallization temperature is of small importance, in some cases, in others it may be the determining factor. An example of this is found in the atent sheathing of insulated telephone cable. According to one process of making such sheathed cable a cold worked aluminum tube is drawn down upon the core of insulated wires. However, in order to provide the necessary ductility in the aluminum sheath the whole cable must be subjected to an annealing operation. A conventional annealing treatment cannot be employed for this purpose because it would destroy or greatly injure the insulation on the wires comprising the cable. It therefore becomes necessary to employ a sheathing which can be softened and made more ductile without damage to the insulation.

It is an object of this invention to provide a wrought aluminum alloy article that has a lower recrystallization temperature than aluminum containing the same impurities in the same amounts as the alloy. Another object is to provide a wrought aluminum alloy article which recrystallizes at a faster rate than aluminum containing the same impurities in the same amount under the same conditions of work and thermal treatment. A further object is to provide a means for lowering the recrystallization temperature of cold worked aluminum alloy articles containing up to 0.8% total of iron and silicon impurities. Another object is to utilize aluminum of a purity commonly produced to form alloy articles having a lower recrystallization temperature than the aluminum without the alloy addition. Still another object is to provide an aluminum cable sheathing which can be annealed without damage to the insulation.

I have discovered that a lower recrystallization temper ature and a higher rate of recrystallization can be obtained in a wrought aluminous article by forming the article of an aluminum alloy consisting essentially of aluminum, at least 0.01% each of iron and silicon, the total of the two elements not exceeding 0.3%, the amount of iron not exceeding the proportion of 4 parts of iron to 3 parts of silicon, a maximum of 0.05% each of copper and magnesium as impurities and 0.005 to 0.25% beryllium than by using aluminum containing the same impurities in the same quantity and worked to the same extent but with no beryllium addition. By observing the foregoing iron and silicon ratio together with making the beryllium addition it has been possible to obtain a recrystallization temperature in a cold worked article which is as much as F. lower than that of aluminum of the same purity without the addition of beryllium and which has received the same amount of cold work. To state the matter differently, the cold worked aluminum-beryllium alloy product can be annealed at a lower temperature or in a shorter time at a higher temperature than the same article made of aluminum containing the same kind and amount of impurities as those occurring in the alloy. Moreover, the results of annealing the cold Worked alloy articles have been found to be uniform which is of considerable importance from the standpoint of manufac turing operations.

Control of the iron and silicon impurities within the specified limits is essential to the production of a wrought article having the low recrystallization characteristic. While the minimum amount of iron and silicon should be 0.01% of each, the total should not exceed 0.3% of the weight of the alloy. in an alloy having less than 0.01% each of iron and silicon nothing is gained by adding beryllium as far as reducing the recrystallization temperature is concerned. On the other hand, if more than a total of 0.8% of these impurities is present, the beryllium addition has no substantial effect on the temperature of recrystallization. To secure the best results, the minimum amount of iron and silicon should be 0.03% of each and the total should, preferably, be within the range of 0.1 to 0.5%. Within the foregoing ranges foriron and silicon, the iron content should not be more; than $5 of the silicon content and to obtain the best re sults it should not exceed of the amount of silicon. In the latter case, the minimum amount of silicon would be proportionately higher than 0.01% and in preferred pr t ss he m mum n nt nt hou d e 0.03% hi the lowest silicon content should be 0.04%. Unless the ratio of iron to silicon is observed the benefit from the beryllium addition is greatly reduced.

In regard to other impurities, any copper and mag; nesium should be kept at a minimum, the maximum amount of each not exceeding 005%, as mentioned above. Still other impurities, such as manganese, titanium, zirconium, molybdenum, chromium and vanadium may be present but in very small amounts, usually less than 0.01% each, and the total should not exceed 0.02%. In these amounts they do not offset the beneficial effect of beryllium upon the recrystallization temperature.

The addition of 0.005 to 0.25% beryllium to aluminum of the purity defined above and having the proper ratio of iron to silicon has the surprising effect of producing an alloy having a lower temperature of recrystallization and a higher rate of recrystallization when used in the form of a worked article than prevails in the absence of beryllium. The addition of alloying elements to aluminum ha always been found to raise the recrystallization temperature and hence the discovery of the opposite effect of beryllium is indeed surprising. No explanation of this result is offered. To obtain the optimum benefit from the beryllium, 0.01 to 0.1% should be used, especially Where the iron impurity is less than of the silicon content. The beryllium addition can be made in any one of the conventional ways of introducing the metal.

As stated above, the amount of cold work influences the temperature at which recrystallization will occur. In order to obtain the lowest recrystallization temperature, the alloy articles should receive a reduction in thickness of not less than 20% or be given an equivalent minimum amount of cold work. A reduction in thickness of at least 40% or an equivalent amount of cold work is usually desired while reductions or cold work exceeding 90% are preferred. Such reductions are not difiicult to obtain in commercial practice for the alloy is easily fabricated, and in some instances no intermediate annealing may be required in producing the final shape from an ingot.

One of the advantages of my invention rests in the increase in rate of recrystallization which can be obtained at temperatures where aluminum without beryllium is annealed. Thus, if one does not wish to take advantage of the lowest possible annealing temperature permitted by the addition of beryllium, a higher temperature can be used and obtain a considerable reduction in the length of time required to effect complete recrystallization. It is well known in annealing aluminum, for example, that with but slight cold working a very long period of time may be required to bring about complete recrystallization. Also, even Where the cold Working is severe the rate of recrystallization may be low if the annealing temperature is very close to the temperature of recrystallization. Under either condition the addition of beryllium and control of the ratio of iron to silicon will accelerate recrystallization. For example, it has been found that with an aluminum alloy sheet composed of aluminum, 0.02% beryllium, 0.04% iron and 0.04% silicon, which had been cold rolled 90% and annealed at a temperature of 450 B, it was possible to obtain complete recrystallization within a period of minutes, whereas, aluminum sheet of the same purity and with the same amount of cold work must be heated at 600 F. to produce complete recrystallization in the same, length of time.

The rate of recrystallization is determined by noting when new grains first form and the time elapsed until substantially all of the grain fragments have formed new grains. Such a determination is most conveniently carried out by testing a series of samples cut from the samesheet- 4 or other article, heating them to a given temperature and removing the samples at specified time intervals and observing the extent to which recrystallization has occurred. Although the presence of new grains can be microscopically detected upon a proper etching of the metal, it is advisable to supplement the examination with an X-ray determination.

The elfect of beryllium upon the recrystallization temperature of cold rolled sheets of the alloy is illustrated in the following examples. Two grades of aluminum were used as the base metal. One identified as A, contained 0.03% iron and 0.04% silicon and the other, identified as B, contained 0.13% iron and 0.18% silicon. Melts of the two grades of metal were prepared and different amounts of beryllium added to a portion of each melt with the exception of the one serving as the blank or control sample. The metal was cast and cold rolled to 0.050" thick sheet with suitable intermediate annealing treatment so that the final product had a reduction in thickness of after the intermediate anneal. Samples of sheet of each composition were heated to and held at a selected temperature for /2 hour. The beryllium content of the sheet samples and the lowest temperatures at which recrystallization Was complete appear in the table below:

Recrystallization Temperaturc, F.

Percent Be Content One of the applications for the aluminum-beryllium product made in accordance with my invention is that of forming a sheath for insulated power and telephone cable. As has been mentioned, the sheathing of such cable has presented a difficult problem because of the necessity for softening the sheath after it has been drawn down upon the insulated wires. It has been found that the alumihum-beryllium product, as defined above, provides a very satisfactory sheath from the standpoints of application to the cable, of being annealed on the cable, and the flexibility of the final cable product. Such advantages, it can be readily appreciated, are of particular importance in providing a seamless sheath on the cable.

This application is a continuation-in-part of my copending application Serial No. 172,001, filed July 3, 1950.

Having thus described my invention and certain embodiments thereof, I claim:

1. An aluminum base alloy article which has received at least 20% cold work, said alloy consisting of 0.005 to 0.25% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.01% each of iron and silicon, the total quantity of iron and silicon not exceeding 0.8% and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cold worked alloy article being characterized by a lower temperature of recrystallization when annealed than aluminum containing only impurities including not less than 0.01% each of iron and silicon and not more than a total of 0.8% of iron and silicon, but the ratio of said iron to silicon exceeding 4 to 3, where said aluminum has received the same amount of cold work as said cold worked article.

2. An aluminum base alloy article which has received atleast 20% cold work, said alloy consisting of 0.005 to 0.25% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.01% each of iron and silicon, the total quantity of iron and silicon not exceeding 0.8% and the amount of iron not exceeding 4 of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cold worked alloy article being characterized by a lower temperature of recrystallization when annealed than aluminum containing only impurities including not less than 0.01% each of iron and silicon and not more than a total of 0.8% of iron and silicon, but the ratio of said iron to silicon exceeding 3 to 4, where said aluminum has received the same amount of cold work as said cold worked article.

3. An aluminum base alloy article which has received at least 20% cold work, said alloy consisting of 0.01 to 0.1% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.03% of iron and 0.04% of silicon, the total quantity of iron and silicon not exceeding 0.5% and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cold worked alloy article being characterized by a lower temperature of recrystallization when annealed than aluminum containing only impurities including not less than 0.01% each of iron and silicon and not more than a total of 0.8% of iron and silicon, but the ratio of said iron to silicon exceeding 3 to 4, where said aluminum has received the same amount of cold Work as said cold Worked article.

4. An aluminum base alloy article which has received at least 40% cold work, said alloy consisting of 0.005 to 0.25% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.01% each of iron and silicon, the total quantity of iron and silicon not exceeding 0.8% and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cold worked alloy article being characterized by a lower temperature of recrystallization when annealed than aluminum containing only impurities including not less than 0.01% each of iron and silicon and not more than a total of 0.8% of iron and silicon, but the ratio of said iron to silicon exceeding 4 to 3, where said aluminum has received the same amount of cold Work as said cold Worked article.

5. An aluminum base alloy article which has received at least 90% cold work, said alloy consisting of 0.01 to 0.1% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.03% of iron and 0.04% of silicon, the total quantity of iron and silicon not exceeding 0.5% and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cold worked alloy article being characterized by a lower temperature of recrystallization when annealed then aluminum containing only impurities including at least 0.03% iron and 0.04% silicon and not more than a total of 0.5 of iron and silicon, but the ratio of said iron to silicon exceeding 3 to 4, where said aluminum has received the same amount of cold Work as said cold worked article.

6. An annealed aluminum base alloy cable sheath which prior to annealing received at least 20% cold Work, said alloy consisting of 0.005 to 0.25% beryllium, a maximum of 0.05 each of copper and magnesium impurities, at least 0.01% each of iron and silicon, the total quantity of iron and silicon not exceeding 0.8% and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cable sheath being characterized by having undergone recrystallization at a lower temperature than aluminum containing only impurities including not less than 0.01% each. of iron and silicon and not more than a total of 0.8% of iron and silicon, but the ratio of said iron to silicon exceeding 4 to 3, where said aluminum has received the same amount of cold Work as said aluminum base alloy cable sheath.

7. An annealed aluminum base alloy cable sheath which prior to annealing received at least cold Work, said alloy consisting of 0.01 to 0.1% beryllium, a maximum of 0.05% each of copper and magnesium impurities, at least 0.01% each of iron and silicon, the total quantity of iron and silicon not exceeding 0.5 and the amount of iron not exceeding of the silicon content, and the balance aluminum except for other impurities than those named hereinbefore, said cable sheath being characterized by having undergone recrystallization at a lower temperature than aluminum containing only impurities including not less than 0.01% each of iron and silicon and not more than a total of 0.5 iron and silicon, but the ratio of said iron to silicon exceeding 3 to 4, Where said aluminum has received the same amount of cold work as said aluminum base alloy cable sheath.

References Cited in the file of this patent UNITED STATES PATENTS 1,716,943 Archer et al June 11, 1929 2,565,768 Gittings Aug. 28, 1951 2,670,309 McClintock Feb. 23, 1954 OTHER REFERENCES Phillips: The Grain Size of Rolled Aluminum, The Journal of the Inst. of Metals, vol. 68, 1942, pages 47-408, particularly pages 83, 89 and 104.

Spillett: The Structure of Rolled and Annealed Aluminum as Revealed by X-Rays, The Journal of the Ins-t. of Metals, vol. 69, 1943, pages 149-175, particularly pages 149 and -163.

Varley: The Recovery and Recrystallization of Rolled Aluminum of Commercial Purity, The Journal of the Inst. of Metals, vol. 75, 1948-1949, pages -202, particularly pages 186 and 194.

Mechanical Properties of Metals and Alloys, Bureau of Standards Circular No. C447 (1943), page 22.

U0 S DEPARTMENT O55 COMMERCE PATENT QFFECE CE'TIFICATE Q) aiECTIQN Patent No, 2 826518 March 11, 1958 William Aa Andaman It is hereby certified. that error appears in the printed specification of the above numbered patent requiring correction and that the said Let oers Patent should read as corrected beluw.

Column 2, lines 34 and. 60, for "093%" read m 068% in each occurrence Signed and sealed thifi' 6th clay of 1.958,

(SEMI) Atfiest:

KARL nosam c. wusou Atteating Officer Commissioner of Patents 

1. AN ALUMINUM BASE ALLOY ARTICLE WHICH HAS RECIEVED AT LEAST 20% COLD WORK, SAID ALLOY CONSISTING OF 0.005 TO 0.25% BERYLLIUM, A MAXIMUM OF 0.05% EACH OF COPPER AND MAGNESIUM IMPURITIES, AT LEAST 0.01% EACH OF IRON AN SILICON, THE TOTAL QUANTITY OF IRON AND SILICON NOT EXCEEDING 0.8% AND THE AMOUNT OF IRON NOT EXCEEDING 4/3 OF THE SILICON CONTENT, ANS THE BALANCE ALUMINUM EXCEPT FOR OTHER IMPURITIES THAN THOSE NAMED HEREINBEFORE, SAID COLD WORKED ALLOY ARTICLE BEING CHARACTERIZED BY A LOWER TEMPERATURE OF RECRYSTALLIZATION WHEN ANNEALED THAN ALUMINUM CONTAINING ONLY IMPURITIES INCLUDING NOT LESS THAN 0.01% EACH OF IRON AND SILICON AND NOT MORE THAN A TOTAL OF 0.8% OF IRON AND SILICON BUT THE RATIO OF SAID IRON TO SILICON EXCEEDING 4 TO 3 WHERE SAID ALUMINUM HAS RECIEVED THE SAME AMOUNT OF COLD WORK AS SAID COLD WORKED ARTICLE. 